AMC has renewed The Walking Dead for a fourth season -- without showrunner Glen Mazzara, who has parted ways with cable's top series.

"Both parties acknowledge that there is a difference of opinion about where the show should go moving forward, and conclude that it is best to part ways. This decision is amicable and Glen will remain on for postproduction on season 3B as showrunner and executive producer," AMC said in a statement. (Filming on season three has already concluded, with the second half of episodes set to return to AMC in February.)

A replacement has yet to be announced but sources tell THR that the series may elevate a current member of the show's writing staff.

Mazzara's contributions to the zombie drama have been widely hailed by critics, with the series landing on several critics' Best of 2012 lists and being praised for its turnaround in pacing -- THR deemed the series a 2012 Rule Breaker for its willingness to take big swings including killing off major characters midseason.

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Mazzara becomes the latest in a line of showrunner issues at AMC, which most recently re-renewed third-year drama Hell on Wheels after creators/showrunners Joe and Tony Gayton departed the Western and John Shiban was poised to return. However, he recently exited the series with John Wirth tapped the drama's third showrunner in as many seasons. In addition, Rubicon creator/showrunner Jason Horwitch exited the series in 2010. The cable network also went through protracted contract negotiations with Breaking Bad's Vince Gilligan and Mad Men's Matt Weiner, which are also said to have turned contentious after rumored budget cuts.

I thought it was pretty messed up when they canned Darabont. That said, the pilot was amazing and everything after was meh. Then AMC cut the budget despite it being a hit for them.

Mazzarra really turned around the 2nd half of S2 and S3 was on another level to this point. A little disturbing that they either pushed him elsewhere for monetary reasons or he felt like it was necessary. It's pretty much the biggest (non-NFL) cable show of all time. Not sure how you let that walk away.